Abstract
Acetylacetone (AA), which has two tautomers (diketo and enol), has been found to be a potent photo-activator for wastewater treatment. However, the crucial structural characteristics in the photo-activity remained unclear. Herein, the performance of 16 AA derivatives and structural analogues (AAs) was extensively evaluated for a real dyeing wastewater and a model dye solution under UV irradiation. The results indicate that the straight-chain aliphatic 1,3-diketone structure was crucial in the high-rate photobleaching. Photo-induced direct electron transfer by enolic AAs and indirect electron transfer with free radicals generated from the cleavage of ketone AAs were the two main mechanisms. The substituents affect the keto-enol tautomerization and the charge population, thereby influencing the photochemical activity of AAs. Electron-donating groups (e.g., -CH3, -(CH3)2, -CH2CH3) at the central carbon in AAs would increase the content of the diketone form and promote the generation of organic radicals from α-cleavage. By contrast, the presence of electron-withdrawing groups (such as -Cl, -(F)3, and -C2H4Br) might lead to the hydrolysis or hydration of AAs, and consequently depressed the photobleaching rate. The results here are valuable for the design of more efficient and eco-friendlier photo-activators for environmental remediation based on diketone photochemistry.
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